1. Field of the Invention
The present invention relates to a lens shape machining method and a lens shape machining device for carrying out a measurement along a spiral path as well as a machining in the machining by the spiral path.
2. Description of the Related Art
In an ultra-precision machining, a compensation machining on the basis of an onboard measurement is essential for achieving a shape precision of a nanometer unit. The compensation machining on the basis of the onboard measurement is mainly carried out frequently in an optical device such as a lens or the like. The conventional lens metal mold is generally machined and compensated by machining the lens metal mold on the basis of a lathe machining, and compensating and machining an error of a shape on the basis of the onboard measurement.
On the basis of popularization of a cell phone and a smart phone and development of various high-density integrated sensors in recent years, a numerical quantity of a compact lens which is mounted on these products is increased. Accordingly, a lot of high-precision lens metal molds which are used for manufacturing the compact lens are going to be required. In the conventional lathe machining which machines the lens metal mold one by one, it is impossible to achieve a production capacity which can respond to the needs, and it is necessary to achieve a simultaneous machining of a lot of compact high-precision lenses, and a simultaneous machining of several thousands of lens arrays in some cases, for meeting the demand of the compact lens.
Consequently, it is often the case that a spiral path machining according to a milling is applied to the machining for meeting the demand of the compact lens. Since the spiral path machining comes to the lathe machining in a pseudo manner, it is an optimum machining method in the lens array machining. Further, for example, Japanese Patent Application Laid-Open No. 2007-276049 discloses a technique in which an array shape metal mold is machined by a scan machining, and a measurement using an onboard measuring device and a machining compensation on the basis of the result of measurement are carried out along a linear raster path.
In the machining of the lens array metal mold, the machining according to the spiral machining path has been conventionally carried out. On the other hand, the measurement and the compensation have been conventionally handled only by a cruciform section measurement (refer to FIG. 19). In the cruciform section measurement, it is possible to comprehend an outline tendency of vertical and lateral asymmetries of the shape, however, it is impossible to comprehend the other portions than the portion which is measured in the crisscross manner. Even if a compensated machining amount is determined according to an approximating method, a space therebetween is too large, so that it is highly likely that a compensation which is away from an actual shape error is applied.
The three-dimensional measurement and machining according to the raster path (an aggregation of the linear paths) which is disclosed in Japanese Patent Application Laid-Open No. 2007-276049 mentioned above can measure all the machining surfaces, and can machine the high-precision lens array metal mold. However, since the measurement and the machining are carried out along the linear path, a line of a linear feeding of a tool tends to be left on the machining surface, and there is a case that a micro line adversely affects an optical characteristic. Further, since there are a lot of motions such as an escaping motion and the like which are neither an effective machining nor a measuring motion, for changing to the next path after finishing one path, reduction of a man hour is prevented.